1. Field of the Invention
The invention relates to frames for backpacks and knapsacks and to methods of making those frames.
2. Description of Related Art
Many backpacks and knapsacks have rigid or semirigid frames that act to suspend the backpack load and distribute it more evenly to the wearer's body. Some frames also allow a user to secure or cinch gear to his or her back more easily than with a backpack alone. Backpack frames may be either internal to the backpack or external to it.
Traditionally, external backpack frames have been made of metal tubes, such as aluminum or steel tubes. These types of frames are simple to construct, as the tubes are simply welded together, but they are typically very heavy, and thus reduce the effective load that a user can carry.
Internal backpack frames are generally made to be lighter, but problems typically arise in making an internal frame that has a useful combination of strength and flexibility. Some degree of flexibility in a backpack frame can help to cushion the user against shifts in the load as he or she walks or runs and to “decouple” the backpack load from the user and his or her movements. However, the problem is multifaceted, because there are some places in a backpack frame where strength and stiffness are warranted in order to properly support the backpack load.
One solution to the stiffness/flexibility problem is to use different materials for different parts of the backpack frame, and some manufacturers have attempted to do so. However, conventional attempts to use many different materials in the same frame often become so complex that they are difficult to manufacture and maintain.